A Department of Energy researcher at the Oak Ridge National Laboratory studies the coronavirus in this photo from June 2020. Since then, the COVID-19 virus has mutated into several variants and the latest, the delta variant, has been called the “fastest and fittest” for its high transmissibility rate. (Photo by Genevieve Martin/U.S. Department of Energy)

August 4, 2021

Cronkite News

Here’s what makes the COVID-19 delta variant different, and dangerous

After a brief period of decline, COVID-19 cases are back on the rise in the United States and experts say the delta variant, now deemed to be as contagious as the chickenpox, is to blame.

Delta, the name for the variant officially known as B.1.617.2, is a mutation of the original coronavirus strain. Originating in India, the World Health Organization called delta the “fastest and the fittest” in regard to its rapid spread.

As a result, new cases of COVID-19 have skyrocketed: Nationally, new cases jumped from an average of 14,438 a day in the first week of June to 72,493 per day in the last week of July, according to the Centers for Disease Control and Prevention, while in Arizona, cases rose from an average 425 a day to 1,595 a day in the same period, according to the Arizona Department of Health Services.

READ ALSO: Daily COVID-19 cases in Arizona more than double in July

That surge led to a new push for vaccinations – while there have been relatively small numbers of delta variant infections among people who have been vaccinated, the vast majority of new infections, hospitalizations and deaths occurs among the unvaccinated. But after an initial scramble for vaccines, the number of vaccinations leveled off, with just 57.8% of Americans having received at least one dose as of this week, and 52.2% of Arizonans.

Arizona has not imposed new restrictions, but several states have. President Joe Biden announced last week that federal workers and contractors would either have to show proof of vaccination or face routine testing and be required to wear a mask, among other restrictions.

Given the aggressiveness of the delta variant, the CDC recommended last week that anyone, even people who have been vaccinated, wear a mask when indoors in a public place if they are in an area with “high” or “substantial” virus transmission.

Fourteen of Arizona’s 15 counties fall in one of those categories. Only Cochise County is in the moderate transmission range, while Graham, Pima and Yuma counties have substantial transmission rates and every other county has a high rate, of 100 new cases or more per 100,000 residents.

The CDC estimates the delta variant of the coronavirus that causes COVID-19 is responsible for more than 82% of cases in the U.S, up from 50% reported the first week of July.

Yale Medicine reported delta is 50% more transmissible than the alpha variant, which was already 50% more transmissible than the original strain. Alpha first surfaced in the United Kingdom and only accounts for 9% of cases in the U.S., according to the CDC.

People who are not vaccinated face the most risk of infection, but according to ABC15 Health Insider Dr. Shad Marvasti, traditional precautions should be taken by vaccinated people as well, including wearing a mask indoors and social distancing when possible.

“I think this is the wisest thing to do because we want to keep the economy open,” Marvasti told ABC15. “We want to keep our kids in school. We don’t want to shut anything down, but we know masks work, whether vaccinated or unvaccinated, masks will work. They will protect you from the delta variant.”

It is possible to get infected while vaccinated, but preliminary data shows two doses of the Pfizer or Moderna vaccine appeared to be about 88% effective against disease and 96% effective against hospitalization with the delta variant, according to Public Health England.

“We are seeing higher rates of hospitalizations … in people who are unvaccinated, but we’re seeing more positive cases of breakthrough with people who are fully vaccinated,” Marvasti told ABC15. “I think we should take a better-safe-than-sorry approach.”

Cronkite News has partnered with ABC15 Arizona to expand the station’s Health Insider series, which provides expert advice and insights into health topics. Cronkite News is experimenting with storytelling tools and techniques to help explain the issues. Find more of our explainer videos here.


Story by Jamie Landers, Cronkite News